Semiconductor transistors, in particular field-effect controlled switching devices such as a Metal Oxide Semiconductor Field Effect Transistor (MOSFET) and an Insulated Gate Bipolar Transistor (IGBT) have been used for various applications including but not limited to use as switches in power supplies and power converters, electric cars, air-conditioners, and even stereo systems. Particularly with regard to power devices capable of switching large currents and/or operating at higher voltages, low on-state resistance Ron and high breakdown voltages are often desired.
To increase the breakdown voltage of lateral field-effect transistors, for example of an LDMOS (Lateral Diffused Metal Oxide Semiconductor device) manufactured using a double diffusion process and with drain, drift and source regions extending to a main surface, a field electrode may be arranged on a field oxide extending along the drift region next to the main surface. The field oxide may be formed using a LOCOS process (LOCal Oxidation of Silicon). The breakdown voltage of the semiconductor devices with such a field redistributing structure is mainly determined by the dielectric properties and the vertical thickness of the field oxide.
However, thicker field oxides may increase the on-state resistance Ron. In particular when semiconductor structures of different rated breakdown voltages are to be integrated in a single integrated semiconductor device, for example a power transistor and a measuring circuitry and or a logic circuitry formed in CMOS-technology (complementary MOS) or BiCMOS-technology (combing bipolar junction transistors and CMOS transistors) such as BCD-technology (Bipolar-CMOS-DMOS), the on-state resistance Ron of the semiconductor transistors with lower rated blocking voltage may significantly be increased when corresponding field oxides are formed in a common LOCOS-process.
Accordingly, there is a need to improve field redistributing structures of lateral semiconductor devices and manufacturing methods therefor.